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If you have service with Verizon Wireless, what happens next may give your location away to the burglar -- your cell phone sounds a tone. It turns out Verizon Wireless phones are designed to do this.

This all started with a story out of Austin, Texas back in November when Carol, who did not give her last name, came home and saw that the chain to her property had been cut. Afraid that someone dangerous was on her land, Carol grabbed her cell phone to call 911.

"And I dialed and the alarm went off," she said.

That's right, her phone sounded a tone. It wasn't an ear-splitting sound, but loud enough to give away someone trying to hide.

"I was afraid the criminals were down the driveway and that they would hear," Carol said.

We investigated and found out that this 911 tone service is limited to Verizon.

Working with the 911 call center in Seattle, we tested four different phones on the Verizon network. Each phone made a tone when we dialed 911 and when we ended the call.

Why would Verizon have its phones do this? It turns out it's how the company interpreted an FCC regulation to make wireless phones accessible to users with disabilities.

"So if someone who did call 911 was disabled, they would actually know that the calls did go through, if they were visually impaired and the tone would go off. And that was the intent of it," said Georgia Taylor with Verizon.

After hearing about the Austin case, Verizon decided to change its policy. Some time later this year, the phones it sells will be reprogrammed.

"The default will be off. So then you can turn it to vibrate if you want that or you can have the tone as well," Taylor said.

The change will leave the customers in charge of the 911 tone option, Taylor said.

Verizon points out correctly that cell phones have helped many people caught in domestic violence situations. The company says before the incident in Texas, not a single customer had complained about the 911 tone feature.

Verizon will make the the change to the new cell phones it sells some time this summer. But as for the millions of phones the company has already sold, they cannot be changed. Even if the phone is set on vibrate, it will still ring when you call 911.

And please believe me on this and don't try dialing 911 yourself. We made special arrangements with the dispatch center for our test.